The present invention relates to PEM fuel cells and, more particularly, to corrosion-resistant terminal collector plates and methods for making the same.
Fuel cells have been proposed as a power source for electric vehicles and other applications. One known fuel cell is the PEM (i.e., Proton Exchange Membrane) fuel cell that includes a so-called xe2x80x9cmembrane-electrode-assemblyxe2x80x9d comprising a thin, solid polymer membrane-electrolyte having an anode on one face of the membrane-electrolyte and a cathode on the opposite face of the membrane-electrolyte. The anode and cathode typically comprise finely divided carbon particles, having very finely divided catalytic particles supported on the internal and external surfaces of the carbon particles, and proton conductive material intermingled with the catalytic and carbon particles.
The membrane-electrode-assembly is sandwiched between a pair of electrically conductive contact elements which serve as current collectors for the anode and cathode, and may contain appropriate channels and openings therein for distributing the fuel cell""s gaseous reactants (i.e., H2 and O2/air) over the surfaces of the respective anode and cathode.
Bipolar PEM fuel cells comprise a plurality of the membrane-electrode-assemblies stacked together in electrical series while being separated one from the next by an impermeable, electrically conductive contact element known as a bipolar plate or septum. The septum or bipolar plate has two working faces, one confronting the anode of one cell and the other confronting the cathode on the next adjacent cell in the stack, and each bipolar plate electrically conducts current between the adjacent cells. Contact elements at the ends of the stack are referred to as end, terminal, or collector plates. These terminal collectors contact a conductive element sandwiched between the terminal bipolar plate and the terminal collector plate.
As can be seen, the terminal collector plate serves many functions, including, sealing the stack, providing electrical conductivity, permitting ingress and egress of fluids, and providing a stable material between the stack and the external environment. There remains the challenge to optimize as many of these functions as possible, and as cost-effectively as possible.
The present invention provides an electrochemical cell stack having a terminal collector end plate that has both an electrically conductive and a non-conductive region. The non-conductive region contains at least one aperture for fluid communication into and out of the stack. The non-conductive region is coated with a protective coating that is corrosion-resistant. Such a coating may comprise a passivation layer, a corrosion-resistant polymeric coating, or both.
In another embodiment of the present invention, the electrically conductive region of the terminal plate is coated with a conductive protective layer, comprising a conductive oxidation resistant metal layer. Optionally, the oxidation resistant metal layer may be further coated with a conductive oxidation-resistant polymeric coating.
Another aspect of the present invention includes methods for treating the terminal plate to provide corrosion resistance in the non-conductive region. Further aspects of methods of treatment include protecting the conductive region of the terminal plate with an oxidation resistant polymer coating that contains conductive particles.
Further areas of applicability of the present invention will become apparent from the detailed description provided hereinafter. It should be understood that the detailed description and specific examples, while indicating the preferred embodiment of the invention, are intended for purposes of illustration only and are not intended to limit the scope of the invention.